1. Field of the Invention
This invention relates to an improved electrostatographic imaging process, an apparatus used in the above process and an imaging member. More specifically, the improved electrostatographic imaging process of this invention involves treating the imaging surface of the photoconductor or imaging member of the electrostatographic apparatus with a lubricating effective amount of at least one compound selected from the group consisting of phthalic acid, isophthalic acid, terephthalic acid, the metal and ammonium salts thereof. By providing a film of lubricant over substantially all of the imaging surface, transfer and removal of toner particles from the imaging surface is facilitated.
2. Description of the Prior Art
The formation and development of images on the surface of photoconductive materials by electrostatic means is well known. The basic xerographic process as taught by C. F. Carlson in U.S. Pat. No. 2,297,691, involves placing a uniform electrostatic charge on a photoconductive insulating layer, exposing the layer to a light and shadow image to dissipate the charge on the areas of the layer exposed to the light and developing the resulting latent electrostatic image by depositing on the image a finely divided electroscopic material referred to in the art as "toner". The toner will normally be attracted to those areas of the layer which retain a charge, thereby forming a toner image corresponding to the latent electroscopic image. This powder image may then be transferred to a support surface such as paper. The transferred image may subsequently be permanently affixed to the support surface by heat. Other suitable fixing means such as solvent or overcoating treatment may be substituted for the foregoing heat fixing step.
Many methods are known for applying the electroscopic particles to the latent electrostatic image to be developed. One development method as disclosed by E. N. Wise in U.S. Pat. No. 2,618,552 is known as "cascade" development. In this method, developer material comprising relatively large carrier particles having finely divided toner particles electrostatically clinging to their surface is conveyed to and rolled or cascaded across the latent electrostatic image bearing surface. The composition of the toner particles is so chosen as to have a triboelectric polarity opposite that of the carrier particles. In order to develop a negatively charged latent electrostatic image, an electroscopic powder and carrier combination should be selected in which the powder is triboelectrically positive in relation to the carrier. Conversely, to develop a positively charged latent electrostatic image, the electroscopic powder and carrier should be selected in which the powder is triboelectrically negative in relation to the carrier. This triboelectric relationship between the powder and carrier depends on their relative positions in a triboelectric series where the materials are arranged in such a way that each material is charged with a positive electrical charge when contacted with any material below it in the series and with a negative electrical charge when contacted with any material above it in the series. As the mixture cascades or rolls across the image bearing surface, the toner particles are electrostatically deposited and secured to the charged portions of the latent image and are not deposited on the uncharged or background portions of the image. Most of the toner particles accidentally deposited in the background are removed by the rolling carrier, due apparently, to the greater electrostatic attraction between the toner and the carrier than between the toner and the discharged background. The carrier particles and unused toner particles are then recycled. This technique is extremely good for the development of line copy images.
Another technique for developing electrostatic images is the "magnetic brush" process as disclosed, for example, in U.S. Pat. No. 2,874,063. In this method, a developer material containing toner and magnetic carrier particles is carried by a magnet. The magnetic field of the magnet causes alignment of the magnetic carriers in a brush-like configuration. This "magnetic brush" is engaged with an electrostatic image bearing surface and the toner particles are drawn from the brush to the electrostatic image by electrostatic attraction. Many other methods such as "touchdown" development, as disclosed by C. R. Mayo in U.S. Pat. No. 2,895,847, are known for applying electroscopic particles to electrostatic latent images to be developed. The development processes, as mentioned above, together with numerous variations, are well known to the art through various patents and publications and through the widespread availability and utilization of electrostatographic imaging equipment.
In automatic xerographic equipment, it is conventional to employ a xerographic plate in the form of an endless imaging surface, which is continuously rotated through a cycle of sequential operations including charging, exposing, developing, transfer and cleaning. The plate is usually charged by means of a corona generating device of the type disclosed by L. E. Walkup in U.S. Pat. No. 2,777,957, which is connected to a suitable source of high potential. After forming a powder image on the electrostatic latent image during the development step, the powder image is electrostatically transferred to a support surface by means of a corona generating device, such as the corona device mentioned above. In automatic equipment employing a rotating drum, a receiving surface, to which a powder image is to be transferred, is moved through the equipment at the same rate as the periphery of the drum and contacts the drum at the transfer position interposed between the drum surface and the corona generating device. Transfer is effected by a corona generating device which imparts an electrostatic charge to attract the powder image from the drum to the support surface. The polarity of charge required to effect image transfer is dependent upon the visual form of the original copy relative to the reproduction and the electroscopic characteristics of the developing material employed to effect development. For example, where a positive reproduction is to be made of a positive original, it is conventional to employ a positive polarity corona to effect transfer of a negatively charged toner image to a receiving surface. When a positive reproduction from a negative original is desired, it is conventional to employ a positively charged developing material which is repelled by the charged areas on the plate and deposits on the discharged areas to form a positive image which may be transferred by negative polarity corona. In either case, a residual powder image usually remains on the plate after transfer. Before the plate may be reused for a subsequent cycle, it is necessary that the residual image be removed to prevent "ghost images" from forming on subsequent copies and to prevent residual film buildup on the photoreceptor. In the positive to positive reproduction process described above, the residual developer powder is tightly retained on the plate surface by a phenomenon that is not fully understood but believed to be caused by an electrical charge that prevents complete transfer of the powder to the receiving surface, particularly in the image area. This charge is substantially neutralized by means of a corona generating device prior to contact of the residual powder image with a cleaning device. The neutralization of the charge enhances the cleaning efficiency of the cleaning device.
Various electrostatographic plate cleaning devices such as "brush" cleaning apparatus and "web" type cleaning apparatus are known in the prior art. A typical brush cleaning apparatus is disclosed by L. E. Walkup et al in U.S. Pat. No. 2,832,977. Brush type cleaning means usually comprise one or more rotating brushes, which brush residual powder from the plate into a stream of air which is exhausted through a filtering system. A typical web cleaning device is disclosed by W. P. Graff, Jr, et al in U.S. Pat. No. 3,186,838. As disclosed by Graff, Jr. et al, removal of the residual powder from the plate is effected by passing a fibrous web material over the plate surface.
The sensitivity of the imaging member to abrasion, however, requires that special precautions be exercised during the cleaning phase of the copying cycle. For example, pressure contact between cleaning webs and imaging surfaces must be kept to a minimum to prevent rapid destruction of the imaging surface. Although thick protective coatings would protect the imaging surfaces for longer periods of time, the electrical properties of the imaging member layer impose certain limitations as to the acceptable maximum thickness of the coating. Since thick protective coatings are normally applied by conventional coating techniques, including the use of a film forming material suspended in a solvent, considerable inconvenience, expense and time is involved in removing the photoreceptor from the machine, preparing the eroded photoreceptor surface for reception of a new coating, applying the new coating, allowing the new coating to dry and reinstalling the newly coated photoreceptor into the machine. Certain extremely thin films, applied to the imaging surface as a pretreatment or in situ during the machine sequence, have been successful, however, the art is constantly on the lookout for improved films or at least practical alternatives. Furthermore, for reasons which are not entirely clear, toner particles are frequently difficult to remove from some photoreceptor coating materials, and toner accumulation causes deterioration of subsequent images formed on the photoreceptor surface in reusable imaging systems. Thus, there is a continuing need for a better system for protecting imaging surfaces, developing electrostatic latent images and removing residual developed images.
It is, therefore, the objective of this invention to provide an improved imaging process and system to overcome the above noted deficiencies in the prior art.
A more specific objective of this invention is to provide an improved electrostatographic imaging process permitting greater ease of transfer and removal of toner particles from the surface of the imaging member.
Another of the objectives of this invention is to provide an improved imaging member having an adherent film of lubricant over substantially all of its imaging surface.
Still yet another of the objectives of this invention is to provide an apparatus for carrying out the above process.